The invention relates to a method for, and apparatus for use in, the manufacture of laminated glass articles.
A laminated glass article may comprise two or more glass sheets with an interlayer of transparent plastics material between each pair of glass sheets. The plastics material is normally thermoplastic and after assembly between the glass sheets is bonded thereto by the application of heat and pressure. Such laminated glass sheet material is commonly used in cases where safety glass is required, such as vehicle windscreens or windows. To achieve a satisfactory laminated product, it is necessary for the glass sheets and plastics interlayer to bond together over the entire area of the glass sheets and for the bonding to be such that in use, delamination does not occur. To achieve this it is necessary for the plastics interlayer to fill the entire space between the glass sheets and for the glass sheets to be drawn together over their whole area during the bonding process. It has previously been proposed in the manufacture of such a laminated glass article to apply reduced pressure to the peripheral edge of the assembly of sheets where the junction between the glass sheets and interlayer is exposed, prior to commencing the bonding action. In a known process the assembly is subjected to ambient pressure and temperature during which stage trapped air is drawn out of the interlayer from between the glass sheets. The assembly is then heated to a temperature at which the interlayer becomes tacky, e.g. 90.degree.C, during which stage further de-airing of the interlayer occurs and a preliminary bonding is brought about between the glass sheets and the interlayer by the glass sheets being drawn together under the ambient external pressure about the trapped interlayer. This has however been a preliminary treatment, called a prenip process, which is carried out as the first stage of a two stage process, the full bonding being effected in the second stage of the process. In the second stage, the glass sheet assembly is further heated to effect proper bonding and is thereafter cooled In some cases it is desirable to transfer the glass sheet assembly to a suitable pressure vessel for the second stage where the temperature and pressure are raised to carry out the full bonding operation.